Swift: Use absl::StrJoin to dump arguments for logging.

This also removes the TODO about using `absl::StrJoin` to dump the environment because we can't easily get a range from a null-terminated `envp`. It also doesn't suffer from the usual awkwardness around inserting a separator *between* elements but not after the last one, so a for loop is clear enough.

Author: sashabu

swift/extractor/BUILD.bazel

@@ -16,6 +16,7 @@ swift_cc_binary(
         "//swift/extractor/remapping",
         "//swift/extractor/translators",
         "//swift/third_party/swift-llvm-support",
+        "@absl//absl/strings",
     ],
 )
 

swift/extractor/main.cpp

@@ -9,6 +9,8 @@
 #include <swift/FrontendTool/FrontendTool.h>
 #include <swift/Basic/InitializeSwiftModules.h>
 
+#include "absl/strings/str_join.h"
+
 #include "swift/extractor/SwiftExtractor.h"
 #include "swift/extractor/infra/TargetDomains.h"
 #include "swift/extractor/remapping/SwiftFileInterception.h"
@@ -184,18 +186,13 @@ codeql::SwiftExtractorConfiguration configure(int argc, char** argv) {
   return configuration;
 }
 
-// TODO: use `absl::StrJoin` or `boost::algorithm::join`
 static auto argDump(int argc, char** argv) {
-  std::string ret;
-  for (auto arg = argv + 1; arg < argv + argc; ++arg) {
-    ret += *arg;
-    ret += ' ';
+  if (argc < 2) {
+    return ""s;
   }
-  ret.pop_back();
-  return ret;
+  return absl::StrJoin(argv + 1, argv + argc, " ");
 }
 
-// TODO: use `absl::StrJoin` or `boost::algorithm::join`
 static auto envDump(char** envp) {
   std::string ret;
   for (auto env = envp; *env; ++env) {